One of the most common navigation watches produced, with many used by the U.S. military well into the Cold War era.

Credit: National Air and Space Museum, Smithsonian Institution

Tools of the Trade

Army Air Forces navigators in World War II benefited from a wide range of tools and equipment.

Many of the tools they used first appeared in simpler forms during the 1930s. Besides P. V. H. Weems and Harold Gatty, several other innovators deserve recognition for their contributions in developing the equipment that was essential to sustaining long-range air operations.

Albert Hegenberger did the most within the Army Air Corps in the interwar years to advance the state of navigational equipment. Thomas Thurlow worked hard on the eve of World War II to ensure that newly minted 20-year-old navigators had the training and experience in this equipment to perform effectively. And Curtis LeMay helped make the navigator an essential crewmember on bomber aircraft.

Here is a sample of what they used in their celestial and dead reckoning navigation.

The compact A-10 was one of the most commonly used sextants in the Army Air Forces. Tens of thousands were made during World War II, and many remained in service with the Air Force through the 1950s. Key features include a lighted bubble and a recording disk to determine averages.

The British-invented astrograph helped navigators determine the altitude curves of principal stars by projecting reels of film corresponding to certain latitudes. Suspended above the chart table in medium and heavy American bombers, the astrograph quickly fell out of favor because it was heavy and unreliable.

The astrocompass was mainly used to determine magnetic variation in the angular difference between an aircraft’s bearing to the magnetic North Pole and the geographic North Pole. Charles Blair used this one on the first trans-polar solo flight in 1951.

The Air Position Indicator (API) was a remarkable electromechanical system of dead reckoning. It took inputs from airspeed sensors and gyro magnetic compasses and continuously computed latitude and longitude. This system became standard on the American B-29. The API foreshadowed the future importance of computing in navigation.

This pair of Weems-type second-setting “avigation” watches in a shock-mounted case dates from about 1934. One maintained Greenwich Civil Time (later Greenwich Mean Time). The other kept Local Civil Time.

The A-12 sextant was designed with Weems’ assistance just before World War II and manufactured by Ed Link, of Link trainer fame. It represented a new generation of “averaging” sextants that compensated for “Dutch roll” in airplanes by taking multiple sightings and computing an average without manual calculations.